1. Field of the Invention
The invention relates to a bicycle brake device, more particularly to a brake arm with an adjustable applied force ratio for a bicycle brake device.
2. Description of the Related Art
Referring to FIG. 1, a conventional brake arm 10 for a bicycle brake device is shown to have an arm body 11 with a wire attaching unit 110 provided on an upper end portion, a pivot hole 116 formed in a lower end portion, and a shoe mounting portion 114 between the upper and lower end portions. A brake shoe 13 is attached to the mounting portion 114. The wire attaching unit 110 is adapted to be secured to a pull wire of the bicycle brake device (not shown), whilst a fastener extends through the pivot hole 116 to secure the arm body 11 to a bicycle (not shown). When a brake lever of the bicycle brake device is pulled, the pull wire applies a pulling force on the brake arm 10, thereby causing the latter to pivot and enable the brake shoe 13 to contact a wheel of the bicycle.
The ratio of the force that is applied by the brake shoe 13 to the bicycle wheel to the force that is applied by the pull wire to the brake arm 10 is equal to the ratio of the distance (a) between the wire attaching unit 110 and the pivot hole 116 to the distance (b) between the shoe mounting portion 114 and the pivot hole 116. Thus, assuming that the force that is applied to the brake arm 10 remains constant, a stronger braking effect is obtained when the distance ratio (a/b) is larger, while a weaker braking effect is obtained when the distance ratio (a/b) is smaller.
Since the distance ratio (a/b) of the conventional brake arm 10 cannot be adjusted, the applied force ratio of the conventional brake arm 10 is similarly non-adjustable. Therefore, the conventional brake arm 10 is unsuited for use in mountain bicycles, which require a brake arm with an applied force ratio that can be varied in accordance with the road conditions.